Apparatus for storing and/or transporting high level radioactive waste, and method for manufacturing the same

ABSTRACT

A system for storing and/or transporting high level radioactive waste, and a method of manufacturing the same. In one aspect, the invention is a ventilated vertical overpack (“VVO”) having specially designed inlet ducts that refract radiation back into the storage cavity. A clear line-of-sight does not exist through the inlet ducts and, thus, the canister can be supported on the floor of the VVO. Also disclosed is a method of manufacturing a variable height VVO that falls within a regulatory license previously obtained for a shorter and taller version of the VVO.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/175,899, filed May 6, 2009, the entirety ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to apparatus, systems andmethods for storing and/or transporting high level radioactive waste,and specifically to such apparatus, systems and methods that utilize aventilated vertical overpack that allows natural convection cooling ofthe high level radioactive waste, which can be spent nuclear fuel(“SNF”) in certain instances.

BACKGROUND OF THE INVENTION

In the operation of nuclear reactors, it is customary to remove fuelassemblies after their energy has been depleted down to a predeterminedlevel. Upon removal, this SNF is still highly radioactive and producesconsiderable heat, requiring that great care be taken in its packaging,transporting, and storing. In order to protect the environment fromradiation exposure, SNF is first placed in a canister, which istypically a hermetically sealed canister that creates a confinementboundary about the SNF. The loaded canister is then transported andstored in a large cylindrical container called a cask. Generally, atransfer cask is used to transport spent nuclear fuel from location tolocation while a storage cask is used to store SNF for a determinedperiod of time.

In a typical nuclear power plant, an open empty canister is first placedin an open transfer cask. The transfer cask and empty canister are thensubmerged in a pool of water. SNF is loaded into the canister while thecanister and transfer cask remain submerged in the pool of water. Oncethe canister is fully loaded with SNF, a lid is placed atop the canisterwhile in the pool. The transfer cask and canister are then removed fromthe pool of water. Once out of the water, the lid of the canister iswelded to the canister body and a cask lid is then installed on thetransfer cask. The canister is then dewatered and backfilled lied withan inert gas. The transfer cask (which is holding the loaded canister)is then transported to a location where a storage cask is located. Theloaded canister is then transferred from the transfer cask to thestorage cask for long term storage. During transfer of the canister fromthe transfer cask to the storage cask, it is imperative that the loadedcanister is not exposed to the environment.

One type of storage cask is a ventilated vertical overpack (“VVO”). AVVO is a massive structure made principally from steel and concrete andis used to store a canister loaded with spent nuclear fuel. TraditionalVVOs stand above ground and are typically cylindrical in shape and areextremely heavy, often weighing over 150 tons and having a heightgreater than 16 feet. VVOs typically have a flat bottom, a cylindricalbody having a cavity to receive a canister of SNF, and a removable toplid.

In using a VVO to store SNF, a canister loaded with SNF is placed in thecavity of the cylindrical body of the VVO. Because the SNF is stillproducing a considerable amount of heat when it is placed in the VVO forstorage, it is necessary that this heat energy have a means to escapefrom the VVO cavity. This heat energy is removed from the outsidesurface of the canister by ventilating the VVO cavity. In ventilatingthe VVO cavity, cool air enters the VVO chamber through bottomventilation ducts, flows upward past the loaded canister as it is warmedfrom the heat emanating from the canister, and exits the VVO at anelevated temperature through top ventilation ducts. Such VVOs do notrequire the use of equipment to force the air flow through the VVO.Rather, these VVOs are passive cooling systems as they use the naturalair flow induced by the heated air to rise within the VVO (also know asthe chimney effect).

While it is necessary that the VVO cavity be vented so that heat canescape from the canister, it is also imperative that the VVO provideadequate radiation shielding and that the SNF not be directly exposed tothe external environment. The inlet duct located near the bottom of theoverpack is a particularly vulnerable source of radiation exposure tosecurity and surveillance personnel who, in order to monitor the loadedVVOs, must place themselves in close vicinity of the ducts for shortdurations. Therefore, when a typical VVO is used to store a canister ofSNF in its internal cavity, the canister is supported in the cavity sothat the bottom surface of the canister is higher than the top of inletventilation ducts. This is often accomplished by providing supportblocks on the floor of the cavity. By positioning the bottom surface ofthe canister above the inlet ventilation ducts, a line of sight does notexist from the canister to the external atmosphere through the inletventilation ducts, thus eliminating the danger of radiation shine out ofinlet ventilation ducts. However, as discussed below, positioning acanister in the cavity of a VVO so that the bottom surface of thecanister is above the top of the inlet ventilation ducts creates twoissues: (1) a potential cooling problem during a “smart flood”condition; and (2) an increased height of the VVO.

Subpart K of 10 C.F.R. §72 provides for a “general certification” ofcasks for on-site storage of SNF. A number of casks have been licensedby the United States Nuclear Regulatory Committee (“U.S.N.R.C.”) and arelisted in subpart L of 10 C.F.R. §72. These casks are certified to storea whole class of SNF (including SNF coming from pressurized waterreactors (PWRs) or boiling water reactors (BWRs)). Unfortunately,reactors burn fuel in a wide variety of lengths. For example, PWRs inthe U.S. presently burn fuel as short as 146″ (e.g., Ft. Calhoun) and aslong as 198″ (e.g., South Texas). A general certified cask has beenlicensed in one or two fixed lengths (models) by the U.S.N.R.C. However,if the SNF is too long to fit in a licensed cask, then the cask simplycannot be used. Moreover, if the SNF is too short, then axial spacersare used to fill the open space in the storage cells to limit themovement of SNF in the axial direction. Thus, most casks and canistersused in the on-site storage of SNF have significant open spaces in theirstorage cells. This condition is particularly undesirable for VVOsbecause of the adverse consequence to the occupational dose to the plantpersonnel and cost (because of physical modifications forced on theplant), as set forth below.

First, the dose received by the workers performing the loadingoperations is directly influenced by the amount of shielding materialper unit length in the body of the cask. The total quantity of shieldingthat can be installed in a transfer cask is governed by the liftingcapacity of the plant's cask crane. A longer than necessary transfercask means less shielding per unit length installed in the cask which inturn results in increased dose to the workers.

In VVOs, the VVO is often loaded inside the plant's truck bay bystacking the transfer cask over the VVO. Minimizing the height of theVVO's body is essential to allow the VVO to be moved out through theplant's truck bay (typically, a roll-up door) after the canister isinstalled therein. The loaded VVO is typically moved out across theroll-up door without its lid, and the lid is then installed on itimmediately after the VVO body clears the door. Therefore, a keyobjective in the storage VVO design is to minimize the height of VVObody.

In another variation, the transfer cask itself is taken outside throughthe plant's truck bay and carried over to a pit where the transfer ofthe canister to the VVO takes place. In this case, the height of thetransfer cask must be short enough to clear the plant's roll-up door toavoid the need to shorten the transfer cask (or alternatively, toincrease the height of the roll-up door). Shortening the transfer caskis not always possible.

SUMMARY OF THE INVENTION

The present invention, in one aspect, is a ventilated overpack havingspecially designed inlet ducts that allow a canister loaded with SNF (orother high level radioactive waste) to be positioned within the overpackso that a bottom end of the canister is below a top of the inlet ductswhile still preventing radiation from escaping through the inlet ducts.This aspect of the present invention allows the overpack to be designedwith a minimized height because the canister does not have to besupported in a raised position above the inlet ducts within the cavityof the overpack. Thus, it is possible for the height of the cavity ofthe overpack to be approximately equal to the height of the canister,with the addition of the necessary tolerances for thermal growth effectsand to provide for an adequate ventilation space above the canister.

When the canister is supported within the overpack cavity so that thebottom end of the canister is below the top end of the inlet ducts, thecanister is protected from over-heating during a “smart flood” conditionbecause a substantial portion of the canister will become submerged inthe flood water prior to the incoming air flow from the inlet duct beingchoked off. Moreover, the design and arrangement of inlet ducts of theinventive overpack result in the cooling air flow within the overpack tonot be significantly impacted by high wind conditions exterior to theoverpack.

In one embodiment, the invention can be an apparatus for transportingand/or storing high level radioactive waste comprising: an overpack bodyhaving an outer surface and an inner surface forming an internal cavityabout a longitudinal axis; a base enclosing a bottom end of the cavity;a plurality of inlet ducts in a bottom of the overpack body, each of theinlet ducts extending from an opening in the outer surface of theoverpack body to an opening in the inner surface of the overpack body soas to form a passageway from an external atmosphere to a bottom portionof the cavity; a columnar structure located within each of the inletducts, the columnar structures dividing each of the passageways of theinlet ducts into first and second channels that converge at the firstand second openings, wherein for each inlet duct a line of sight doesnot exist between the opening in the inner surface of the overpack bodyand the opening in the outer surface of the overpack body; a lidenclosing a top end of the cavity; and a plurality of outlet ducts, eachof the outlet ducts forming a passageway from a top portion of thecavity to the external atmosphere.

In another embodiment, the invention is an apparatus for transportingand/or storing high level radioactive waste comprising: a cylindricalradiation shielding body forming an internal cavity and having avertical axis; a base enclosing a bottom end of the cavity; a pluralityof inlet ducts in a bottom of the radiation shielding body, each of theinlet ducts forming a horizontal passageway from an external atmosphereto a bottom portion of the cavity; a radiation shielding structurelocated within each of the inlet ducts that divides the horizontalpassageway of the inlet duct into at least first and second horizontallyadjacent portions and blocks a line of sight from existing from thecavity to the external atmosphere through the inlet duct; a radiationshielding lid enclosing a top end of the cavity; and a plurality ofoutlet ducts, each of the outlet ducts forming a passageway from a topportion of the cavity to the external atmosphere.

In another aspect, the invention is directed to a method of utilizing ageneral license obtained for two different ventilated vertical overpacksto manufacture a third ventilated vertical overpack that is covered bythe general license without filing an application for certification ofthe third ventilated vertical overpack.

In one embodiment, the invention can be a method of manufacturing alicensed ventilated vertical overpack without filing an application forcertification comprising: designing a first ventilated vertical overpackcomprising: a first cavity for receiving a first canister containinghigh level radioactive waste, the first cavity having a first horizontalcross section and a first height; a first ventilation system forfacilitating natural convection cooling of the first canister within thefirst cavity, the first ventilation system comprising a first pluralityof inlet vents for introducing cool air into a bottom of the firstcavity and a first plurality of outlet vents for allowing heated air toescape from a top of the first cavity; and wherein the first ventilatedvertical overpack is designed to withstand an inertial load resultingfrom a postulated tip-over event so as to maintain the integrity of thefirst canister within the cavity; designing a second ventilated verticaloverpack comprising: a second cavity for receiving a second canistercontaining high level radioactive waste, the second cavity having asecond horizontal cross section that is the same as the first horizontalcross section and a second height that is less than the first height; asecond ventilation system for facilitating natural convective cooling ofthe second canister within the second cavity, the second ventilationsystem comprising a second plurality of inlet vents for introducing coolair into a bottom of the second cavity and a second plurality of outletvents for allowing heated air to escape from a top of the second cavity,wherein the second plurality of inlet vents have the same configurationas the first plurality of inlet vents and the second plurality of outletvents have the same configuration as the first plurality of outletvents; and wherein the second ventilated vertical overpack is designedto achieve a heat rejection capacity; obtaining a license from aregulatory agency for the first and second ventilated verticaloverpacks; manufacturing a third ventilated vertical overpackcomprising: a third cavity for receiving a third canister containinghigh level radioactive waste, the third cavity having a third horizontalcross section that is the same as the first and second horizontal crosssections and a third height that is less than the first height andgreater than the second height; a third ventilation system forfacilitating natural convective cooling of the third canister within thethird cavity, the third ventilation system comprising a third pluralityof inlet vents for introducing cool air into a bottom of the thirdcavity and a third plurality of outlet vents for allowing heated air toescape from a top of the third cavity, wherein the third plurality ofinlet vents have the same configuration as the first and secondplurality of inlet vents, and the third plurality of outlet vents havethe same configuration as the first and second plurality of outletvents; and wherein the third ventilated vertical overpack isautomatically covered by the license without filing a new applicationfor certification with the regulatory agency.

In another embodiment, the invention can be a method of manufacturing alicensed ventilated vertical overpack without filing an application forcertification comprising: designing a first ventilated vertical overpackhaving a first cavity for receiving a first canister containing highlevel radioactive waste and having a structural configuration that canwithstand an inertial load resulting from a postulated tip-over event soas to maintain the integrity of the first canister within the cavity,the first cavity having a first height that corresponds to a height ofthe first canister; designing a second ventilated vertical overpackhaving a second cavity for receiving a second canister containing highlevel radioactive waste and an inlet and outlet duct configuration forfacilitating natural convective cooling of the second canister thatachieves a heat rejection capacity, the second cavity having a secondheight that corresponds to a height of the second canister, the firstheight being greater than the second height; obtaining a license from aregulatory agency for the first and second ventilated verticaloverpacks; manufacturing a third ventilated vertical overpackcomprising: a third cavity for receiving a third canister containinghigh level radioactive waste, the third cavity having a third heightthat corresponds to a height of the third canister, the third heightbeing greater than the second height and less than the first height; astructural configuration that is the same as the structuralconfiguration of the first ventilated vertical overpack; and an inletand outlet duct configuration for facilitating natural convectivecooling of the third canister that is the same as the inlet and outletduct configuration of the second ventilated vertical overpack; andwherein the first, second and third cavities have the same horizontalcross-sections and the first, second and third canisters have the samehorizontal cross-sections; wherein the third ventilated verticaloverpack is automatically covered by the license without filing a newapplication for certification with the regulatory agency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of VVO according to an embodiment ofthe present invention.

FIG. 2 is top perspective view of the VVO of FIG. 1 with the lid removedand a canister partially loaded within the VVO, wherein a section of theVVO and the canister is cut-away to facilitate viewing.

FIG. 3 is a top view of the VVO of FIG. 1.

FIG. 4 is a vertical cross-sectional view of the VVO of FIG. 1 takenalong view X-X of FIG. 3.

FIG. 5 is a close-up view of area V-V of FIG. 4 illustrating the detailof one of the inlet ducts, taken along a vertical reference plane thatincludes a central axis of the VVO.

FIG. 6 is horizontal cross-sectional view of the VVO of FIG. 1 takenalong horizontal reference plane D-D of FIG. 4.

FIG. 7 is a horizontal cross-sectional view of the lid of the VVO ofFIG. 1.

FIG. 8 is vertical cross-sectional view of the VVO of FIG. 1 with amulti-purpose canister (“MPC”) positioned within the cavity of the VVOaccording to an embodiment of the present invention.

FIG. 9 is the horizontal cross-sectional view of FIG. 6 with an MPCpositioned within the cavity of the VVO according to an embodiment ofthe present invention.

FIG. 10 is a cutaway perspective view of the VVO of FIG. 1 with an MPCpositioned within the cavity of the VVO and with the natural convectivecooling of the MPC schematically illustrated.

FIG. 11 is a cutaway perspective view of an MPC according to anembodiment of the present invention wherein the internal thermosiphonflow of inert gas within the MPC is schematically illustrated.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1-4 concurrently, a ventilated vertical overpack(“VVO”) 1000 according to an embodiment of the present invention isillustrated. The VVO 1000 is a vertical, ventilated, dry, SNF storagesystem that is fully compatible with 1000 ton and 125 ton transfer casksfor spent fuel canister transfer operations. The VVO 1000 can, ofcourse, be modified and/or designed to be compatible with any size orstyle of transfer cask. Moreover, while the VVO 1000 is discussed hereinas being used to store SNF, it is to be understood that the invention isnot so limited and that, in certain circumstances, the VVO 1000 can beused to transport SNF from location to location if desired. Moreover,the VVO 1000 can be used in combination with any other type of highlevel radioactive waste.

The VVO 1000 is designed to accept a canister for storage at anIndependent Spent Fuel Storage Installation (“ISFSI”). All canistertypes engineered for the dry storage of SNF can be stored in the VVO1000. Suitable canisters include multi-purpose canisters (“M PCs”) and,in certain instances, can include thermally conductive casks that arehermetically sealed for the dry storage of high level radioactive waste.Typically, such canisters comprise a honeycomb basket 250, or otherstructure, to accommodate a plurality of SNF rods in spaced relation. Anexample of an MPC that is particularly suited for use in the VVO 1000 isdisclosed in U.S. Pat. No. 5,898,747 to Krishna Singh, issued Apr. 27,1999, the entirety of which is hereby incorporated by reference.

The VVO 1000 comprises two major parts: (1) a dual-walled cylindricaloverpack body 100 which comprises a set of inlet ducts 150 at or nearits bottom extremity and an integrally welded baseplate 130; and (2) aremovable top lid 500 equipped with radially symmetric outlet vents 550.The overpack body 100 forms an internal cylindrical storage cavity 10 ofsufficient height and diameter for housing an MPC 200 fully therein. Asdiscussed in greater detail below, the VVO 1000 is designed so that theinternal cavity 10 has a minimized height that corresponds to a heightof the MPC 200 which is to be stored therein. Moreover, the cavity 10preferably has a horizontal (i.e., transverse to the axis A-A)cross-section that is sized to accommodate only a single MPC 200.

The overpack body 100 extends from a bottom end 101 to a top end 102.The base plate 130 is connected to the bottom end 101 of the overpackbody 100 so as to enclose the bottom end of the cavity 10. An annularplate 140 is connected to the top end 102 of the overpack body 100. Theannular plate 140 is ring-like structure while the base plate 130 isthick solid disk-like plate. The base plate 130 hermetically enclosesthe bottom end 101 of the overpack body 100 (and the storage cavity 10)and forms a floor for the storage cavity 10. If desired, an array ofradial plate-type gussets 112 may be welled to the inner surface 121 ofan inner shell 120 and a top surface 131 of the base plate 130. In suchan embodiment, when the MPC 200 is fully loaded into the cavity 10, theMPC 200 will rest atop the gussets 112. The gussets 112 have top edgesthat are tapered downward toward the vertical central axis A-A. Thus,the gussets 112 guide the MPC 200 during loading and help situate theMPC 200 in a co-axial disposition with the central vertical axis A-A ofthe VVO 1000. In certain embodiments; the MPC 200 may not rest on thegussets 112 but rather may rest directly on the top surface 131 of thebase plate 130. In such an embodiment, the gussets 112 may still beprovided to not only act as guides for properly aligning the MPC 200within the cavity 10 during loading but also to act as spacers formaintaining the MPC 200 in the desired alignment within the cavity 10during storage.

By virtue of its geometry, the overpack body 100 is a rugged,heavy-walled cylindrical vessel. The main structural function of theoverpack body is provided by its carbon steel components while the mainradiation shielding function is provided by an annular plain concretemass 115. The plain concrete mass 115 of the overpack body 100 isenclosed by concentrically arranged cylindrical steel shells 110, 120,the thick steel baseplate 130, and the top steel annular plate 140. Aset of four equispaced steel radial connector plates 111 are connectedto and join the inner and outer shells 110, 120 together, therebydefining a fixed width annular space between the inner and outer shells120, 110 in which the plain concrete mass 115 is poured.

The plain concrete mass 115 between the inner and outer steel shells120, 110 is specified to provide the necessary shielding properties (drydensity) and compressive strength for the VVO 1000. The principalfunction of the concrete mass 115 is to provide shielding against gammaand neutron radiation. However, the concrete mass 115 also helps enhancethe performance of the VVO 1000 in other respects as well. For example,the massive bulk of the concrete mass 115 imparts a large thermalinertia to the VVO 1000, allowing it to moderate the rise in temperatureof the VVO 1000 under hypothetical conditions when all ventilationpassages 150, 550 are assumed to be blocked. The case of a postulatedfire accident at an ISFSI is another example where the high thermalinertia characteristics of the concrete mass 115 of the VVO 1000controls the temperature of the MPC 200. Although the annular concretemass 115 in the overpack body 100 is not a structural member, it doesact as an elastic/plastic filler of the inter-shell space.

Four threaded steel anchor blocks (not illustrated) are also provided atthe top of the overpack body 100 for lifting. The anchor blocks areintegrally welded to the radial plates 111, which join the inner andouter shells 120, 110. The four anchor blocks are located at 90° angularspacings around the circumference of the top of the overpack body 100.

While the cylindrical body 100 has a generally circular horizontalcross-section, the invention is not so limited. As used herein, the term“cylindrical” includes any type of prismatic tubular structure thatforms a cavity therein. As such, the overpack body can have arectangular, circular, triangular, irregular or other polygonalhorizontal cross-section. Additionally, the term “concentric” includesarrangements that are non-coaxial and the term “annular” includesvarying width.

The overpack body 100 comprises a plurality of specially designed inletvents 150. The inlet vents 150 are located at a bottom of the overpackbody 100 and allow cool air to enter the VVO 1000. The inlet vents 150are positioned about the circumference of overpack body 100 in aradially symmetric and spaced-apart arrangement. The structure,arrangement and function of the inlet vents 150 will be described inmuch greater detail below with respect to FIGS. 4-6 and 10.

Referring now to FIGS. 1-4 and 7 concurrently, the overpack lid 500 is aweldment of steel plates 510 filled with a plain concrete mass 515 thatprovides neutron and gamma attenuation to minimize skyshine. The lid 500is secured to a top end 101 of the overpack body 100 by a plurality ofbolts 501 that extend through bolt holes 502 formed into a lid flange503. When secured to the overpack body 100, surface contact between thelid 500 and the overpack body 100 forms a lid-to-body interface. The lid500 is preferably non-fixedly secured to the body 100 and encloses thetop end of the storage cavity 10 formed by the overpack body 100.

The top lid 500 further comprises a radial ring plate 505 welded to abottom surface 504 of the lid 500 which provides additional shieldingagainst the laterally directed photons emanating from the MPC 200 and/orthe annular space 50 (best shown in FIG. 9) formed between the outersurface 201 of the MPC 200 and the inner surface 121 of the inner shell120. The ring plate 505 also assists in locating the top lid 500 in acoaxial disposition along axis A-A of the VVO 1000 through itsinteraction with the annular ring 140. When the lid 500 is secured tothe overpack body 100, the outer edge of the ring plate 505 of the lid500 abuts the inner edge of the annular plate 140 of the overpack body100. A third function of the radial ring 501 is to prevent the lid 500from sliding across the top surface of the overpack body 100 during apostulated tipover event defined as a non-mechanistic event for the VVO1000.

As mentioned above, the lid 500 comprises a plurality of outlet vents550 that allow heated air within the storage cavity 10 of the VVO 1000to escape. The outlet vents 550 form passageways through the lid 500that extend from openings 551 in the bottom surface 504 of the lid 500to openings 552 in the peripheral surface 506 of the lid 500. While theoutlet ducts 550 form L-shaped passageways in the exemplifiedembodiment, any other tortuous or curved path can be used so long as aclear line of sight does not exist from external to the VVO 1000 intothe cavity 10 through the inlet ducts 550. The outlet vents 550 arepositioned about the circumference of the lid 500 in a radiallysymmetric and spaced-apart arrangement. The outlet ducts 550 terminatein openings 552 that are narrow in height but axi-symmetric in thecircumferential extent. The narrow vertical dimensions of the outletducts 550 helps to efficiently block the leakage of radiation. It shouldbe noted, however, that while the outlet vents 550 are preferablylocated within the lid 500 in the exemplified embodiment, the outletvents 550 can be located within the overpack body 100 in alternativeembodiments, for example at a top thereof.

Referring briefly to FIG. 10, the purpose of the inlet vents 150 and theoutlet vents 550 is to facilitate the passive cooling of an MPC 200located within the cavity 10 of the VVO 1000 through naturalconvection/ventilation. In FIG. 10, the flow of air is represented bythe heavy black arrows 3, 5, 7. The VVO 1000 is free of forced coolingequipment, such as blowers and closed-loop cooling systems. Instead, theVVO 1000 utilizes the natural phenomena of rising warmed air, i.e., thechimney effect, to effectuate the necessary circulation of air about theMPC 200 stored in the storage cavity 10. More specifically, the upwardflowing air 5 (which is heated from the MPC 200) within the annularspace 50 that is formed between the inner surface 121 of the overpackbody 100 and the outer surface 201 of the MPC 200 draws cool ambient air3 into the storage cavity 10 through inlet ducts 150 by creating asiphoning effect at the inlet ducts 150. The rising warm air 5 exits theoutlet vents 550 as heated air 7. The rate of air flow through the VVO1000 is governed by the quantity of heat produced in the MPC 200, thegreater the heat generation rate, the greater the air upflow rate.

To maximize the cooling effect that the ventilating air stream 3, 5, 7has on the MPC 200 within the VVO 1000, the hydraulic resistance in theair flow path is minimized to the extent possible. Towards that end, theVVO 1000 comprises eight inlet ducts 150 (shown in FIG. 6). Of course,more or less inlet ducts 150 can be used as desired. In one preferredembodiment, at least six inlet ducts 150 are used. Each inlet duct 150is narrow and tall and has an internally refractive contour (shown inFIG. 6) so as to minimize radiation streaming while optimizing the sizeof the airflow passages. The curved shape of the inlet ducts 150 alsohelps minimize hydraulic pressure loss. The structure of the inlet ducts150 will be described below in much greater detail with respect to FIGS.4-6.

Referring back to FIGS. 1-4 and 7 concurrently, in order to decrease theamount of radiation scattered to the environment, an array of ductphoton attenuators (DPAs) may be installed in the inlet and/or outletducts 150, 550. An example of a suitable DPA is disclosed in U.S. Pat.No. 6,519,307, the entirety of which is hereby incorporated byreference. The DPAs scatter any radiation streaming through the ducts150, 550, thereby significantly decreasing the local dose rates aroundthe ducts 150, 550. The configuration of the DPAs is such that theincrease in the resistance to air flow in the air inlet ducts 150 andoutlet ducts 550 is minimized.

The inlet ducts 150 permit the MPC 200 to be positioned directly atopthe top surface 131 of the base plate 130 of the VVO 1000 if desired,thus minimizing the overall height of the cavity 10 that is necessary tohouse the MPC 200. Naturally, the height of the overpack body 100 isalso minimized. Minimizing the height of the overpack body 100 is acrucial ALARA-friendly design feature for those sites where the EgressBays in their Fuel Buildings have low overhead openings in their roll-updoors. To this extent, the height of the storage cavity 10 in the VVO1000 is set equal to the height of the MPC 200 plus a fixed amount toaccount for thermal growth effects and to provide for adequateventilation space above the MPC 200, as set forth in Table 1 below.

TABLE 1 OPTIMIZED MPC, TRANSFER CASK, AND VVO HEIGHT DATA FOR A SPECIFICUNIRRADIATED FUEL LENGTH, l MPC Cavity Height, c l + Δ¹ MPC Height(including top lid), h c + 11.75″ VVO Cavity Height H + 3.5″ OverpackBody Body Height (height from H + 0.5″ the bottom end to the top end ofthe overpack body) Transfer Cask Cavity Height h + 1″ Transfer CaskHeight (loaded over the pad) h + 27″ Transfer Cask Total Height H + 6.5″¹Δ shall be selected as 1.5″ < Δ < 2″ so that c is an integral multipleof ½ inch (add 1.5″ to the fuel length and round up to the nearest ½″ orfull inch).

As can be seen from Table 1, the first step in the height minimizationplan is to minimize the height of the MPCs 200. The MPC cavity height,c, is customized for each plant (based on its fuel) so that there is nounnecessary (wasted) space.

The MPC 200 can be placed directly on the base plate 130 such that thebottom region of the MPC 200 is level with the inlet ducts 150 becauseradiation emanating from the MPC 200 is not allowed to escape throughthe specially shaped inlet ducts 150 due to: (1) the inlet ducts 150having a narrow width and being curved in shape so as to wrap around acolumnar structure 155 made of alloy steel or steel (or a combination ofsteel and concrete); (2) the configuration of the inlet ducts 150 issuch that that there is no clear line of sight from inside the cavity 10to the exterior environment; and (3) there is enough steel and/orconcrete in the path of any radiation emanating from the MPC 200 tode-energize it to acceptable levels. The columnar structure 155 isconfigured to be cylindrical so as to be internally refractive, but itcan also be of rectangular, elliptical, or other prismaticcross-sections to fulfill the essence of the above design features. Withthe radiation streaming problem at the inlet ducts 150 solved, the top102 of the overpack body 100 can be as little as ½″ higher than the topsurface 202 of the MPC 200. Table 1 above gives typical exemplarydimensions but, of course, is not limiting of the present invention.

Finally, with reference to FIG. 4, to protect the concrete mass 115 ofthe VVO 1000 from excessive temperature rise due to radiant heat fromthe MPC 200, a thin cylindrical liner 160 of insulating material, can bepositioned concentric with the inner shell 120. This insulating liner140 is slightly smaller in diameter than the inner shell 120. The lineracts as a “heat shield” and can be hung from top impact absorbers 165 orcan be connected directly to the inner shell 120 or another structure.The insulating layer 140 can be constructed of, without limitation,blankets of alumina-silica fire clay (Kaowool Blanket), oxides ofalimuna and silica (Kaowool S Blanket), alumina-silica-zirconia fiber(Cerablanket), and alumina-silica-chromia (Cerachrome Blanket). Theunderside of the overpack lid 500 may also include a liner of insulatingmaterial if desired.

The top impact absorbers 165 are connected to the inner surface 121 ofthe inner shell 120 in a circumferentially spaced apart arrangement ator near the top end of the cavity 10. Similarly, bottom impact absorbers166 are connected to the inner surface 121 of the inner shell 120 in acircumferentially spaced apart arrangement at or near the bottom end ofthe cavity 10. The top and bottom impact absorbers 165, 166 are designedto absorb kinetic energy to protect the MPC 200 during an impactivecollision (such as a non-mechanistic tip-over scenario). In theexemplified embodiment, the top and bottom impact absorbers 165, 166 arehollow tube like structures but can be plate structures if desired. Theimpact absorbers 165, 166 serve as the designated locations of impactwith the MPC lid 210 and the base plate 220 of the MPC 200 in case theVVO 1000 tips over. The impact absorbers 165, 166 are thin steel memberssized to serve as impact attenuators by crushing (or buckling) againstthe solid MPC lid 210 and the solid MPC base 220 during an impactivecollision (such as a non-mechanistic tip-over scenario).

Referring now to FIGS. 4-6 concurrently, the details of the inlet ducts150 will be discussed in detail. Generally, each of the inlet ducts 150extend from an opening 151 in the outer surface 112 of the overpack body100 (which in the exemplified embodiment is also the outer surface ofthe outer shell 110) to an opening 152 in the inner surface 121 of theoverpack body 100 (which in the exemplified embodiment is also the innersurface of the inner shell 120). Each of the inlet ducts 150 forms apassageway 153 from an atmosphere external to the VVO 1000 to a bottomportion of the cavity 10 so that cool air can enter the cavity 10.

A columnar structure 155 is located within each of the inlet ducts 150.Each of the columnar structures 155 extend along their own longitudinalaxis B-B. In the exemplified embodiment, the longitudinal axes B-B ofthe columnar structures 155 are substantially parallel with the centralvertical axis A-A of the VVO 1000. Thought of another way, thelongitudinal axes B-B extend in the load bearing direction of theoverpack body 100. Of course, the invention will not be so limited inall embodiments and the longitudinal axes B-B of the columnar structures155 may be oriented in a different manner if desired.

The columnar structures 155 are formed by a combination of steel plates156, 157 and concrete 115. The plates 157 are cylindrical in shape andbound the outer circumferences of the columnar structures 155, therebyforming the outer surfaces of the columnar structures 155. The plates156 are flat plates that are thicker than the plates 157 and arecentrally positioned within the columnar structures 155 so as to extendalong the axes B-B. The plates 156 provide structural integrity to thecolumnar structures 155 (similar to rebar) and also add additional gammashielding to the columnar structures 155. The columnar structures 155have a transverse cross-section that is circular in shape. However, theinvention is not so limited and the columnar structures 155 can have atransverse cross-section of any prismatic shape.

The columnar structures 155 divide each of the passageways 153 of theinlet ducts 150 into a first channel 153A and a second channel 153B. Foreach inlet duct 150, the first and second channels 153A, 153B convergeat both openings 151, 152, thereby collectively surrounding the entirecircumference of the outer surface of the columnar structure 155.Thought of another way, for each inlet duct 150, the first and secondchannels 153A, 153B collectively circumferentially surround thelongitudinal axes B-B of the columnar structures 155, forming a circular(or other prismatic) passageway contained within the walls of theoverpack body 100.

Importantly, for each inlet duct 150, a line of sight does not existbetween the opening 152 in the inner surface 121 of the overpack body100 and the opening 151 in the outer surface 112 of the overpack body100. This is because the columnar structures 155 block such aline-of-sight and provide the required radiation shielding, therebypreventing radiation shine into the environment via the inlet ducts 150.As such, the MPC 200 can be positioned within the cavity 10 so as to behorizontally and vertically aligned with the inlet ducts 150 withoutradiation escaping into the external environment (see FIGS. 8-9). Statedconceptually, for each inlet duct 150, the opening 152 in the innersurface 121 of the overpack body 100 is aligned with the opening 151 inthe outer surface 112 of the overpack body 100 so that: (i) a firstreference plane D-D that is perpendicular to the longitudinal axis A-Aof the overpack body 100 intersects both the opening 152 in the innersurface 121 of the overpack body 100 and the opening 151 in the outersurface 112 of the overpack body 100; and (ii) a second reference planeC-C that is parallel with and includes the longitudinal axis A-A of theoverpack body 100 intersects both the opening 152 in the inner surface121 of the overpack body 100 and the opening 151 in the outer surface112 of the overpack body 100. When an MPC 200 is positioned in thecavity 10 as shown in FIGS. 8-9, the MPC 200 is also intersected by thereference plane C-C and the reference plane D-D.

The inlet vents 150 (and thus the first and second channels 153A, B) arelined with steel. For each inlet duct 160, the steel liner includes thecylindrical plate 157 of the columnar structure 155, two arcuate wallplates 158, an annular roof plate 159, and the base plate 130. Allconnections between these plates can be effectuated by welding. As canbest be seen in FIGS. 5 and 6, the width of the first and secondchannels 153A, B is defined by a gap located between the cylindricalplate 157 of the columnar structure 155 and the two arcuate plates 158.Preferably, the cylindrical plate 157 of the columnar structure 155 andthe two arcuate plates 158 are arranged in a concentric and evenlyspaced-apart manner so that the first and second channels 153A, B have aconstant width. Most preferably, the first and second channels 153A, Bare curved so as to reduce hydraulic pressure loss. Finally, it is alsopreferred that the inlet ducts 150 have a height that is at least threetimes that of its width.

Referring now to FIGS. 8-11 concurrently, the benefits achieved by thespecial design of the inlet ducts 150 with respect to MPC 200 storagewill be discussed. During use of the VVO 1000, an MPC 200 is positionedwithin the cavity 10. An annular gap 50 exists between the outer surface201 of the MPC 200 and the inner surface 121 of the overpack body 100The annular gap 50 creates a passageway along the outer surface 201 ofthe MPC 200 that spatially connects the inlet vents 150 to the outletvents 550 so that cool air 3 can enter VVO 1000 via the inlet vents 150,be heated within the annular space 50 so as to become warm air 5 thatrises within the annular space 50, and exit the VVO 1000 via the outletvents 550.

The MPC 200 is supported within the cavity 10 so that the bottom surfaceof the MPC 200 rests directly atop the top surface 131 of the base plate130. This is made possible because the inlet ducts 150 are shaped so asnot to allow radiation to shine therethrough because a clearline-of-sight does not exist from the cavity 10 to the atmosphereoutside of the VVO 1000 through the inlet ducts 150. Thus, the cavity 10(and as a result the overpack body 100) can be made as short as possibleand substantially correspond to the height of the MPC 200, as discussedabove with respect to Table 1.

Additionally, positioning the MPC 200 in the cavity 10 so that thebottom surface of the MPC 200 is below the top of the opening 152 of theinlet vents 150 ensures adequate MPC cooling during a “smart floodcondition.” A “smart flood” is one that floods the cavity 10 so that thewater level is just high enough to completely block airflow though theinlet ducts 150. In other words, the water level is just even with thetop of the openings 152 of the inlet ducts 150. Because the bottomsurface of the MPC 200 is situated at a height that is below the top ofthe openings 152 of the inlet ducts 150, the bottom of the MPC 200 willbe in contact with (i.e. submerged in) the water during a “smart flood”condition. Because the heat removal efficacy of water is over 100 timesthat of air, a wet bottom is all that is needed to effectively removeheat and keep the MPC 200 cool. The MPC cooling action effectivelychanges from ventilation air-cooling to evaporative water cooling.Additionally, as shown in FIG. 11, the MPC 200 is particularly suitedfor “smart-flood” cooling because the MPC 200 is designed to achieve aninternal natural thermopshion cyclical flow. Thus, in a smart-flood,”the thermosiphon flow in the MPC 200 will circulate the internal gas sothat the hot gas is circulated to the top of the MPC where its heat canbe effectively removed.

As mentioned above, the design discussed above for the VVO 1000 allowsthe VVO 1000 to be constructed so that the height of the cavity 10 (andthus the VVO 1000) is minimized to the extent possible to accommodate anMPC 200 that, in turn, corresponds in height to the length of the SNFassemblies at issue. It has been further discovered that because the MPC200 does not have to be positioned above the inlet ducts 150, the sameconfiguration of inlet ducts 150 can be used for any and all VVOs 1000,irrespective of the height of the MPC 200 to be positioned therein.Additionally, it has been further discovered that if the outerhorizontal cross-section of the MPC 200 and the inner horizontalcross-section of the VVO 1000 are also kept constant, that it ispossible to manufacture VVOs 1000 of variable heights under a singleN.R.C. (or other regulatory agency) license without having to obtain anew license, so long as a taller and shorter version of the VVO 1000 hasalready been licensed.

Licensing of the shorter VVO 1000 is necessary because the shorter a VVO1000 is, the less effective the heat rejection capacity of that VVO'snatural ventilation system becomes. This is because decreasing theheight of the MPC 200 results in a decreased upward flow of air withinthe annular space 50, thereby reducing the ventilation of the MPC 200.Licensing of the taller VVO 1000 is necessary because the taller a VVO1000 is, the more susceptible it becomes to inertial loading resultingfrom a postulated tip-over event that would destroy the integrity of theMPC 200 within the cavity 10. Stated simply, assuming that theventilation system of the taller and shorter VVOs are held constant, ifthe shorter VVO meets the required heat rejection capacity, it can beassumed that all taller VVOs will also meet the required heat rejectioncapacity. Similarly, assuming that the structural configuration of thetaller and shorter VVOs are held constant, if the taller VVO canwithstand an inertial load resulting from a postulated tip-over eventand maintain the integrity of the MPC within its cavity, it can beassumed that all shorter VVOs will also withstand the inertial loadresulting from the postulated tip-over event and maintain the integrityof the MPC within its cavity. As used herein, the structuralconfiguration of two VVOs are held constant if the structural componentsand arrangements remain the same, with exception of the height of theshells 110, 120 and possibly the diameter of the outer shell 110.

Thus, in on embodiment, the invention is directed to a method ofdesigning embodiments of the VVO 1000 so that its height is variable andgreater than the plant's fuel length by a certain fixed amount. Thus,VVOs 1000 of varying heights can be manufactured under a singleU.S.N.R.C. license and be suitable to store SNF in an optimizedconfiguration at all nuclear plants in the world. An embodiment of thepresent invention will now be described in relation to VVO 1000discussed above with the addition to suffixes “A-C” to distinguishbetween the tall version of the VVO 1000A the short version of the VVO1000B, and the intermediate version of the VVO 10000 respectively.

According to one embodiment of the present invention, a VVO 1000A havinga first cavity 10A for receiving a first MPC 200A containing high levelradioactive waste is designed. This first VVO 1000A comprises astructural configuration that can withstand an inertial load resultingfrom a postulated tip-over event of the VVO 1000A so as to maintain theintegrity of the first MPC 200A within the cavity. The first cavity 10Ahas a first height H1 that corresponds to the height of the first MPC200A as discussed above in relation to Table 1.

A second VVO 1000B having a second cavity 10B for receiving a second MPC200B containing high level radioactive waste is then be designed. Thesecond VVO 1000B comprises a configuration of inlet and outlet ducts150B, 550B for facilitating natural convective cooling of the second MPC200B that achieves a required heat rejection capacity. The second cavity10B has a second height 112 that corresponds to the height of the secondMPC 200B as discussed above in relation to Table 1. The first height H1is greater than the second height 112.

The designs of the first and second VVOs 1000A, 1000B are then submittedto the appropriate regulatory agency, such as the U.S.N.R.C., forlicensing. A license is obtained from the regulatory agency for thefirst and second VVOs 1000A, 10008.

After the licenses are obtained, a third VVO 1000C comprising a thirdcavity 10C for receiving a third MPC 200C containing high levelradioactive waste is manufactured. The third cavity 10C has a thirdheight 113 that corresponds to a height of the third MPC 200C asdiscussed above in relation to Table 1. The third height 113 is greaterthan the second height 112 and less than the first height H1. The VVO1000C is manufactured to have a structural configuration that is thesame as the structural configuration of the first VVO 1000A and aconfiguration of inlet and outlet ducts 150C, 550C for facilitatingnatural convective cooling of the third MPC 200C that is the same as theconfiguration of the inlet and outlet ducts 150B, 550B of the second VVO1000B. The first, second and third cavities 10A, 10B, 10C all have thesame horizontal cross-sections and the first, second and third MPCs200A, 200B, 200C all have the same outer horizontal cross-sections.

Thus, the third VVO 1000C will automatically be covered by the licensegranted for the VVOs 1000A and 1000B without filing a new applicationfor certification with the regulatory agency.

In the example above, the taller VVO 1000A may also be designed tocomprise a configuration of inlet and outlet ducts 150A, 550A forfacilitating natural convective cooling of the second MPC 200B thatachieves a required heat rejection capacity. The configuration of inletand outlet ducts 150A, 550A may be the same as the configuration ofinlet and outlet ducts 150B, 550B of the shorter VVO 1000B. Similarly,the shorter VVO 1000B may also be designed to comprise a structuralconfiguration that can withstand an inertial load resulting from apostulated tip-over event of the VVO 1000B so as to maintain theintegrity of the first MPC 200B within the cavity 10B. The structuralconfiguration of the VVO 1000B may be the same as the structuralconfiguration of the VVO 1000A.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques. It is tobe understood that other embodiments may be utilized and structural andfunctional modifications may be made without departing from the scope ofthe present invention. Thus, the spirit and scope of the inventionshould be construed broadly as set forth in the appended claims.

1. An apparatus for transporting and/or storing high level radioactivewaste comprising: an overpack body having an outer surface and an innersurface forming an internal cavity about a longitudinal axis; a baseenclosing a bottom end of the cavity; a plurality of inlet ducts in abottom of the overpack body, each of the inlet ducts extending from anopening in the outer surface of the overpack body to an opening in theinner surface of the overpack body so as to form a passageway from anexternal atmosphere to a bottom portion of the cavity; a columnarstructure located within each of the inlet ducts, the columnarstructures dividing each of the passageways of the inlet ducts intofirst and second channels that converge at the first and secondopenings, wherein for each inlet duct a line of sight does not existbetween the opening in the inner surface of the overpack body and theopening in the outer surface of the overpack body; a lid enclosing a topend of the cavity; and a plurality of outlet ducts, each of the outletducts forming a passageway from a top portion of the cavity to theexternal atmosphere.
 2. The apparatus of claim 1 wherein the lidcomprises the outlet ducts, each of the outlet ducts extending from anopening in the inner surface of the lid to an opening in the outersurface of the lid.
 3. The apparatus of claim 1 wherein the columnarstructures have a longitudinal axis, wherein the longitudinal axis ofthe columnar structures are substantially parallel with the longitudinalaxis of the overpack body.
 4. The apparatus of claim 1 wherein for eachinlet duct, the opening in the inner surface of the overpack body isaligned with the opening in the outer surface of the overpack body sothat: (i) a first reference plane that is perpendicular to thelongitudinal axis of the overpack body intersects both the opening inthe inner surface of the overpack body and the opening in the outersurface of the overpack body; and (ii) a second reference plane that isparallel with and includes the longitudinal axis of the overpack bodyintersects both the opening in the inner surface of the overpack bodyand the opening in the outer surface of the overpack body.
 5. Theapparatus of claim 1 wherein the columnar structures have a longitudinalaxis, the first and second channels collectively surrounding acircumference of the longitudinal axis of the columnar structures. 6.The apparatus of claim 1 wherein the columnar structures have alongitudinal axis, and wherein the columnar structures have a prismatictransverse cross-section.
 7. The apparatus of claim 6 wherein thelongitudinal axis of the columnar structures are substantially parallelwith the longitudinal axis of the overpack body.
 8. The apparatus ofclaim 1 wherein the first and second channels are curved.
 9. Theapparatus of claim 1 wherein the overpack body comprises an inner shelland an outer shell concentrically arranged so that a gap exists betweenthe inner and outer shells, the gap filled with a radiation shieldingmaterial.
 10. The apparatus of claim 1 wherein for each inlet duct, theopening in the inner surface of the overpack body is aligned with theopening in the outer surface of the overpack body so that a firstreference plane that is perpendicular to the longitudinal axis of theoverpack body intersects both the opening in the inner surface of theoverpack body and the opening in the outer surface of the overpack body.11. The apparatus of claim 10 further comprising a hermetically sealedcanister for containing high level radioactive waste positioned withinthe cavity so that the first reference plane also intersects thecanister.
 12. The apparatus of claim 1 further comprising a hermeticallysealed canister for containing high level radioactive waste positionedwithin the cavity so that a bottom surface of the canister is in surfacecontact with a top surface of the base.
 13. The apparatus of claim 12wherein the cavity has a transverse cross-section that accommodates nomore than one of the canisters.
 14. The apparatus of claim 1 wherein theinlet ducts have a width and a height that is at least three times thewidth.
 15. The apparatus of claim 1 wherein the base is a baseplateconnected to the overpack body.
 16. The apparatus of claim 1 wherein theoverpack body comprises at least six of the inlet vents arranged in acircumferentially spaced and axi-symmetric manner.
 17. An apparatus fortransporting and/or storing high level radioactive waste comprising: acylindrical radiation shielding body forming an internal cavity andhaving a vertical axis; a base enclosing a bottom end of the cavity; aplurality of inlet ducts in a bottom of the radiation shielding body,each of the inlet ducts forming a horizontal passageway from an externalatmosphere to a bottom portion of the cavity; a radiation shieldingstructure located within each of the inlet ducts that divides thehorizontal passageway of the inlet duct into at least first and secondhorizontally adjacent portions and blocks a line of sight from existingfrom the cavity to the external atmosphere through the inlet duct; aradiation shielding lid enclosing a top end of the cavity; and aplurality of outlet ducts, each of the outlet ducts forming a passagewayfrom a top portion of the cavity to the external atmosphere.
 18. Theapparatus of claim 18 further comprising a hermetically sealed canisterfor containing high level radioactive waste positioned within the cavityso that the canister rests atop the base.
 19. A method of manufacturinga licensed ventilated vertical overpack without filing an applicationfor certification comprising: designing a first ventilated verticaloverpack comprising: a first cavity for receiving a first canistercontaining high level radioactive waste, the first cavity having a firsthorizontal cross section and a first height; a first ventilation systemfor facilitating natural convection cooling of the first canister withinthe first cavity, the first ventilation system comprising a firstplurality of inlet vents for introducing cool air into a bottom of thefirst cavity and a first plurality of outlet vents for allowing heatedair to escape from a top of the first cavity; and wherein the firstventilated vertical overpack is designed to withstand an inertial loadresulting from a postulated tip-over event so as to maintain theintegrity of the first canister within the cavity; designing a secondventilated vertical overpack comprising: a second cavity for receiving asecond canister containing high level radioactive waste, the secondcavity having a second horizontal cross section that is the same as thefirst horizontal cross section and a second height that is less, thanthe first height; a second ventilation system for facilitating naturalconvective cooling of the second canister within the second cavity, thesecond ventilation system comprising a second plurality of inlet ventsfor introducing cool air into a bottom of the second cavity and a secondplurality of outlet vents for allowing heated air to escape from a topof the second cavity, wherein the second plurality of inlet vents havethe same configuration as the first plurality of inlet vents and thesecond plurality of outlet vents have the same configuration as thefirst plurality of outlet vents; and wherein the second ventilatedvertical overpack is designed to achieve a heat rejection capacity;obtaining a license from a regulatory agency for the first and secondventilated vertical overpacks; manufacturing a third ventilated verticaloverpack comprising: a third cavity for receiving a third canistercontaining high level radioactive waste, the third cavity having a thirdhorizontal cross section that is the same as the first and secondhorizontal cross sections and a third height that is less than the firstheight and greater than the second height; a third ventilation systemfor facilitating natural convective cooling of the third canister withinthe third cavity, the third ventilation system comprising a thirdplurality of inlet vents for introducing cool air into a bottom of thethird cavity and a third plurality of outlet vents for allowing heatedair to escape from a top of the third cavity, wherein the thirdplurality of inlet vents have the same configuration as the first andsecond plurality of inlet vents, and the third plurality of outlet ventshave the same configuration as the first and second plurality of outletvents; and wherein the third ventilated vertical overpack isautomatically covered by the license without filing a new applicationfor certification with the regulatory agency.
 20. A method ofmanufacturing a licensed ventilated vertical overpack without filing anapplication for certification comprising: designing a first ventilatedvertical overpack having a first cavity for receiving a first canistercontaining high level radioactive waste and having a structuralconfiguration that can withstand an inertial load resulting from apostulated tip-over event so as to maintain the integrity of the firstcanister within the cavity, the first cavity having a first height thatcorresponds to a height of the first canister; designing a secondventilated vertical overpack having a second cavity for receiving asecond canister containing high level radioactive waste and an inlet andoutlet duct configuration for facilitating natural convective cooling ofthe second canister that achieves a heat rejection capacity, the secondcavity having a second height that corresponds to a height of the secondcanister, the first height being greater than the second height;obtaining a license from a regulatory agency for the first and secondventilated vertical overpacks; manufacturing a third ventilated verticaloverpack comprising: a third cavity for receiving a third canistercontaining high level radioactive waste, the third cavity having a thirdheight that corresponds to a height of the third canister, the thirdheight being greater than the second height and less than the firstheight; a structural configuration that is the same as the structuralconfiguration of the first ventilated vertical overpack; and an inletand outlet duct configuration for facilitating natural convectivecooling of the third canister that is the same as the inlet and outletduct configuration of the second ventilated vertical overpack; andwherein the first, second and third cavities have the same horizontalcross-sections and the first, second and third canisters have the samehorizontal cross-sections; wherein the third ventilated verticaloverpack is automatically covered by the license without filing a newapplication for certification with the regulatory agency.